young plums suffering from plum tree diseases

12 Common Plum Tree Diseases & Pests

Plum trees are a beloved fruit tree that add beauty and bounty to orchards and gardens. However, their aesthetic beauty does not make them immune to diseases and pests, and infestations can seriously impact the health and productivity of plum trees. If you’ve already started growing plum trees, understanding plum tree diseases and pests is crucial for maintaining healthy trees and ensuring a fruitful harvest. Fortunately, we have put together this handy guide on common plum tree diseases and pests that can negatively affect your fruit trees. So, no matter what problems with plum trees you are facing, our advice should provide valuable insights on how to effectively manage and prevent them. So, let’s delve into the world of plum tree diseases and pests and learn how to enjoy these beautiful trees and their bountiful harvests.

Common Plum Tree Diseases

plums on diseased plum tree

Plum trees are a fruitful addition to any garden, but, like any plant, they are susceptible to a range of diseases. In the UK, these charming fruit producers can be affected by a variety of plum tree diseases, causing significant problems with the tree’s growth and fruit production. Fortunately, we have gathered identification and treatment information on the most common plum tree diseases to stop a diseased plum tree from creeping up on you.

1. Black Knot

Black Knot is one of the most serious plum tree diseases, and is caused by the pathogen Dibotryon Morbosum. This disease can have a devastating impact on the tree’s health and fruit production, and if left untreated, can lead to the tree’s death.

Identification

Black Knot begins as a small, velvet green knot on the plum tree branches, and usually appears in spring. As the disease progresses, the knot turns black and swollen, and the fungus may girdle the limbs, causing them to die back. In severe cases, Black Knot can even form on the tree’s trunk, making it difficult to save the tree.

Effects

Black Knot can significantly affect the tree’s fruit production, and in severe cases, can completely halt its usable fruit production. The disease gets progressively worse without treatment, and it can spread to neighbouring trees, exacerbating the problem.

Treatment

The best course of action for treating Black Knot is to prune away the infected areas of the tree as soon as the knots appear. You should do this in late winter or early spring, before new growth begins. Infected branches should be cut back to healthy wood, and the wood should be destroyed to prevent the fungus from spreading. In some cases, it may be necessary to remove the entire tree to prevent the disease from spreading to neighbouring trees.

Prevention

To prevent Black Knot from affecting your plum trees, ensure that they are planted in well-drained soil and receive adequate sunlight and air circulation. Additionally, avoid planting trees too close together, and make sure to prune any infected branches as soon as they appear. You can also use fungicides to prevent this plum tree disease, but they should be applied before the tree becomes infected.

2. Plum Pocket

Plum Pocket is a fungal disease that causes significant problems with the fruit production of plum trees. This plum tree disease is easily characterised by the formation of hollow and discoloured fruit, caused by the fungus Taphrina Deformans.

Identification

Plum Pocket is identified by swelling, discoloured, and hollow fruits that signal the onset of the disease. These hollow fruits may be infested and itching to burst, which further spreads the problem. Once established, the disease returns every year, causing ongoing damage to the tree.

Effects

This plum tree disease can significantly affect fruit production, leading to reduced yields and poor-quality fruit. As the fungus invades the developing fruit, you will start to see it become deformed and hollow. Also, Plum Pocket can spread to neighbouring trees, so you may see similar effects on surrounding trees. 

Treatment

Fungicides can be effective in treating Plum Pocket, but you must apply them early in the season, before the fruit sets. However, if the disease is already established, the best course of action is to remove any infected fruit and destroy it to prevent the fungus from spreading. Pruning the tree to improve air circulation and sunlight exposure can also help prevent the disease from taking hold.

Prevention

Prevention is the most effective way to avoid Plum Pocket affecting your plum trees. This can be achieved by planting disease-resistant varieties, pruning the tree to improve air circulation and sunlight exposure, and practising good orchard garden hygiene.

3. Brown Rot

Brown rot is a fungal disease that commonly affects plum trees, causing damage to the fruit and reducing the tree’s productivity. It is caused by the fungus Monilinia Fructicola and can lead to significant problems if left untreated.

Identification

Gardeners are often unaware that this plum tree disease is affecting their garden until green and ripening fruits display spots of brown rot. The disease progresses quickly, and fruits become mummified and cling to the tree. Also, during the spring, the fungus produces spores, which can spread to neighbouring trees.

Effects

Brown rot can significantly impact the fruit production of plum tree’s, leading to reduced yields and poor-quality fruit. The fungus invades the fruit and causes it to rot, making it unsuitable for consumption.

Treatment

The best course of action for treating brown rot is to remove any infected fruit from the tree and dispose of it to prevent the fungus from spreading. Fungicides can also be effective in treating the disease, but they need to be applied early in the season before the fruit sets.

Prevention

Prevention is key to avoiding brown rot in your plum trees. Good orchard hygiene, such as pruning the tree to improve air circulation and sunlight exposure, removing any dead or diseased wood, and keeping the area around the tree clean and free of debris, can help prevent the disease from taking hold. Fungicides can also be used preventatively to protect the tree from the disease.

4. Plum Pox Virus

Plum pox virus is another of the more serious plum tree diseases that affects other stone fruits, such as peaches and cherries, too. It is caused by a virus that is typically transmitted by aphids but can also be spread through grafting of affected plants.

Identification

One of the main symptoms of plum pox virus is the appearance of discoloured rings on leaves and fruits. Infected leaves may also show yellowing, curling, or distortion, and fruit from infected trees may be small, misshapen, and bitter to the taste.

Effects

Once a tree is infected with plum pox virus, there is no cure, and the tree must be removed to prevent the virus from spreading to nearby plants. The disease can have a significant impact on fruit production, leading to reduced yields and poor-quality fruit. Controlling aphids, the primary vector of the virus, is essential to preventing its spread.

Treatment

Unfortunately, there is no treatment for plum pox virus. The best course of action with a plant suffering from these kinds of plum tree diseases in this case is to remove and destroy it to prevent the spread of the virus to other plants.

Prevention

Preventing the spread of plum pox virus involves controlling the aphids that transmit the disease. You can do this through the use of insecticides, as well as by removing any nearby plants that may be infected. It is also important to avoid grafting or replanting with trees from areas known to have the virus.

5. Perennial Canker on Plums

ripe plums unaffected by plum tree diseases

Perennial canker causes damage to the wood of plum trees and reduces their productivity. It is caused by the fungus Leucostoma Cincta and can lead to significant problems if left untreated.

Identification

Perennial canker is identified by the appearance of sunken areas or cankers on the bark of the trunk and branches. The bark may also have a discoloured or dead appearance. Also, the fungus can cause dead wood to develop on the tree, leading to reduced fruit production.

Effects

Perennial canker can significantly impact the tree’s wood production, leading to reduced yields and poor-quality fruit. The fungus invades the wood, causing it to rot and die, making it unsuitable for fruit production.

Treatment

The best course of action for treating perennial canker is to remove any infected wood from the tree and dispose of it to prevent the fungus from spreading. Fungicides can also be effective in treating the disease, but they need to be applied early in the season before the tree becomes infected.

Prevention

Prevention is the key to avoiding perennial canker in your plum trees. Good orchard hygiene, such as pruning the tree to improve air circulation and sunlight exposure, removing any dead or diseased wood, and keeping the area around the tree clean and free of debris, can help prevent the disease from taking hold. Additionally, avoiding mechanical damage to the tree and ensuring proper drainage can also help prevent the disease from spreading.

6. Plum Tree Leaf Spot

Plum tree leaf spot is a bacterial disease that causes damage to the leaves and reduces the tree’s overall health. Our first of several bacterial plum tree diseases is caused by the bacterium Xanthomonas Pruni and can cause serious issues if left untreated.

Identification

The first signs of plum tree leaf spot are small, water-soaked spots on the leaves, which can be easily overlooked. As the disease progresses, the spots become larger, and a red ring can develop around them, giving the appearance of a “target” or “bull’s eye.” Continued infestation results in further leaf damage with holes surrounded by the red ringed bacterial indicator.

Effects

Plum tree leaf spot can significantly impact the tree’s overall health, leading to reduced growth and productivity. The disease invades the leaves and causes them to wither, turn yellow, and eventually fall off the tree. If left untreated, the disease can spread to other parts of the tree, causing further damage.

Treatment

The best course of action for treating plum tree leaf spot is to remove any infected leaves from the tree and dispose of them to prevent the bacteria from spreading. Copper fungicides can also be effective in treating the disease, but they need to be applied early in the season before the disease spreads. In severe cases, pruning the tree to improve air circulation and sunlight exposure can also help reduce the spread of the disease.

Prevention

Prevention is always best to avoid plum tree leaf spot. Good orchard hygiene, such as removing any dead or diseased wood, keeping the area around the tree clean and free of debris, and avoiding overhead irrigation, can help prevent the disease from taking hold. Additionally, using disease-resistant varieties of plum trees can help reduce the risk of infection.

7. Silver Leaf Disease

This fungal disease can affect many different types of trees, but is commonly listed among plum tree diseases. It is caused by the fungus Chondrostereum Purpureum and can have serious consequences if not treated promptly.

Identification

One of the most obvious symptoms of silver leaf disease is a silver sheen on some of the leaves of the affected tree. This sheen is caused by the fungus growing in the leaf tissue and restricting the flow of water and nutrients to the rest of the tree. Another symptom is visible only when branches 3cm/1in or more wide are pruned. There may be a brown stain in the wood, which is a clear indicator of silver leaf disease.

Effects

If left untreated, silver leaf disease can cause significant damage to the affected tree. The fungus grows within the tree and causes the wood to decay, leading to branch dieback and potentially even tree death. The loss of branches and foliage can significantly impact the tree’s overall health and productivity.

Treatment

The best course of action for treating silver leaf disease is to prune away all affected branches and dispose of them immediately. Be sure to disinfect your pruning tools between cuts to prevent the spread of the fungus. If the tree is severely affected, it may need to be removed to prevent the disease from spreading to nearby trees. Fungicides can also be effective in treating the disease, but they need to be applied early in the season before the fungus takes hold.

Prevention

The best way to prevent silver leaf disease is to maintain good tree health and hygiene. Prune the tree regularly to promote good air circulation and sunlight exposure, and avoid overwatering, which can create conditions favourable for fungal growth. If the tree has any wounds, seal them with a pruning sealer to prevent the entry of pathogens. Also, avoid pruning during wet weather as this can promote the spread of the fungus.

8. Powdery Mildew

Powdery mildew is one of the most common plum tree problems, causing a powder-like substance to appear on the leaves, shoots, and flowers of the tree. This disease can weaken the tree and reduce its productivity if left untreated.

Identification

The powdery mildew appears as a white or greyish powder-like substance on the leaves, shoots, and flowers of the tree. As the disease progresses, the leaves may become distorted or stunted, and the affected plant parts may die off.

Effects

Powdery mildew can weaken the tree and reduce its productivity by interfering with the photosynthesis process. The disease also makes the tree more susceptible to secondary infections and pests, such as aphids, that are attracted to weakened trees.

Treatment

The best course of action for treating powdery mildew is to remove the affected plant parts and dispose of them. Fungicides can also be effective in treating the disease, but they need to be applied early in the season before the disease becomes too severe. Additionally, improving air circulation by pruning the tree to allow more sunlight to reach the interior and removing any crowded branches can help prevent the disease from taking hold.

Prevention

Avoiding powdery mildew spreading disease on plum trees in your garden, prevention is essential. Good orchard hygiene, such as pruning the tree to improve air circulation and sunlight exposure, and keeping the area around the tree clean and free of debris, can help prevent the disease from taking hold. Additionally, planting disease-resistant varieties of plum trees and avoiding overhead irrigation can also help prevent the disease.

Common Plum Tree Pests

As well as plum tree diseases, these lovely fruit trees are susceptible to several pests. Unfortunately, there are several common plum tree pests that can have a serious effect on your trees and their fruits, leading to reduced yields and weakened trees. Some of the common plum tree pests include aphids, pigeons, winter moths, and scale insects. Understanding these pests and their identification, effects, treatment, and prevention methods can help mitigate the risks and keep plum trees healthy and thriving. In this section, we will explore these common pests and provide insights on how to manage and prevent these problems with plum trees.

9. Aphids

Aphids are common plum tree pests, and you can identify them by curled up and sticky leaves. Aphids secrete a sugary substance called honeydew, leaving sticky trails in their wake. While they may not cause significant damage on their own, aphids can weaken trees and make them more vulnerable to other plum tree diseases and pests.

Identification

The first signs of aphids attacking plum trees are young leaves curling up, often referred to as Plum Leaf Curl. The aphids themselves are small green, white or light brown insects that can be seen inside the curled leaves. If left unchecked, the aphids can produce a sticky honeydew that attracts other unwanted pests and diseases.

Effects

Aphids can weaken the tree by sucking sap from the leaves and shoots, reducing the tree’s productivity and growth. The honeydew they produce can also lead to the growth of sooty mould, which can further reduce the tree’s photosynthesis ability.

Treatment

The best way to treat aphids on plum trees is to prune and dispose of any heavily infested plant parts, including curled leaves. Insecticidal soaps and oils, as well as neem oil, can be effective in controlling aphid populations. Encouraging natural predators, such as ladybugs and lacewings, can also help reduce aphid populations.

Prevention

Preventing aphid infestations is important for maintaining the health of plum trees. Keeping the area around the tree clean and free of debris, and regularly checking the tree for signs of aphids can help prevent the pests from becoming established. Additionally, improving air circulation by pruning the tree to allow more sunlight to reach the interior and removing any crowded branches can help prevent aphids from taking hold. Avoiding over-fertilizing the tree can also help discourage aphid infestations.

10. Pigeons

Pigeons may be a bit of a nuisance on the street, but, if they become plum tree pests, you’ll curse them in your garden too! These scavenger birds are attracted to the fruits of the tree and can cause significant damage to the harvest. Pigeons may also cause damage to the tree itself by pecking at the bark and causing wounds.

Identification

Identifying pigeons is usually easy due to their distinct physical features. They are medium-sized birds, often grey or brown in colour, with a plump body, short neck, and small head. Their wingspan can range from 24 to 28 inches, and they have a distinctive cooing sound.

Effects

Pigeons can cause significant damage to the plum tree’s harvest by eating the fruit, often before it is fully ripe. They may also cause damage to the tree itself by pecking at the bark, creating wounds that can weaken the tree’s structure and make it more susceptible to disease and pests.

Treatment

There are several methods for treating pigeon infestations in plum trees. One effective method is to install bird netting around the tree, which will prevent the birds from accessing the fruit. Bird repellent sprays and decoys may also be effective in deterring pigeons from the tree. In some cases, it may be necessary to physically remove the birds from the tree or the surrounding area.

Prevention

Preventing pigeons from becoming plum tree pests is important to ensure a healthy harvest. Installing bird netting around the tree before the fruit is ripe can prevent pigeons from accessing the tree. Additionally, removing any food sources that may attract pigeons, such as bird feeders or open garbage cans, can help prevent them from taking up residence in the area. Regular maintenance of the tree, including pruning and removing any dead or diseased branches, can also help make the tree less attractive to pigeons.

11. Winter Moth

immature plums on diseased plum tree

Winter moths are common plum tree pests, particularly in a winter garden. This pest is known for its small green caterpillars that can cause significant damage to the leaves and buds of the tree. The first sign of infestation is the presence of tiny caterpillars on and around the fruit and leaf buds, which can later spin silken threads and hang from the tree twigs.

Identification

The winter moth caterpillar is a small green insect that is typically 1 inch long when fully grown. The pest is most active in the early spring, and the caterpillars can often be seen hanging from the tree twigs or crawling on the leaves. Infested leaves may have holes, and buds may fail to develop.

Effects

Winter moth caterpillars can cause significant damage to plum trees by eating the leaves, buds, and almost all parts of the foliage. The damage can weaken the tree and reduce its productivity, making it more susceptible to other pests and diseases.

Treatment

The best way to control winter moth infestation is to apply a pesticide early in the spring, before the caterpillars become too numerous. Horticultural oil and Bacillus Thuringiensis (Bt) are effective treatments for the pest. Pruning the tree to remove infested plant parts and keeping the area around the tree clean and free of debris can also help prevent the spread of the pest.

Prevention

Preventing winter moth infestation is key to avoiding damage to plum trees. Regularly monitoring the tree for signs of infestation and applying a pesticide early in the spring can help control the pest. Additionally, maintaining good orchard hygiene, such as pruning the tree to improve air circulation and sunlight exposure and keeping the area around the tree clean, can help prevent the pest from taking hold.

12. Scale Insects

When it comes to common plum tree diseases and pests, scale insects are certainly up there. One form of scale insect that can be particularly problematic is the Lecanium Scale. These insects feed on the sap of a twig, branch or leaf, and can cause damage to the tree if left unchecked. They look like pea-sized growths which are purple-brown in colour on stems and young branches.

Identification

The Lecanium Scale can be identified by the pea-sized growths on the tree, which are purple-brown in colour. These scales feed on the sap of the tree and can cause damage to the plant if left unchecked. They can also leave a sticky residue on the plant that can attract other pests and diseases.

Effects

Lecanium Scale can cause significant damage to plum trees by feeding on the sap of the tree. The damage can weaken the tree and reduce its productivity, making it more susceptible to other pests and diseases.

Treatment

The best way to control Lecanium Scale infestations is to apply a pesticide when the young insects are moving about in May or June. Sprays suitable for killing aphids will also kill moving scale insects. If you miss this stage of their lifecycle, a plant oil winter wash treatment can be used in December to January to effectively suffocate many of the overwintering bugs. If your tree is a manageable size, manually removing the scale insects around May when they are visible but have not yet hatched their eggs is also an effective method. Using a toothbrush and diluted washing up liquid can help to remove them.

Prevention

Preventing Lecanium Scale infestation is key to avoiding damage to plum trees. Regularly monitoring the tree for signs of infestation, such as the pea-sized growths, and applying a pesticide early in the spring when the young insects are moving about can help control the pest. Additionally, maintaining good orchard hygiene, such as pruning the tree to improve air circulation and sunlight exposure and keeping the area around the tree clean, can help prevent the pest from taking hold.

Dealing With Plum Tree Diseases & Pests In Your Garden

Plum tree diseases and pests can cause significant problems for both amateur and professional orchardists. However, by regularly monitoring trees, maintaining good orchard hygiene, and taking appropriate action when necessary, you can control or prevent many plum tree diseases and pests. By following best practices and seeking help when needed, orchardists can enjoy healthy and productive plum trees for years to come.

FAQs

What Does A Diseased Plum Tree Look Like?

A diseased plum tree may exhibit various symptoms depending on the type of disease. Some common signs of a plum tree diseases include stunted growth, yellowing or browning of leaves, wilting, cracked bark, and cankers on the trunk or branches.

How Do You Treat A Plum Tree Diseases?

The treatment for plum tree diseases depends on the specific disease. Fungal diseases can often be treated with fungicides, while bacterial diseases may require pruning or removal of affected plant parts. In some cases, the entire tree may need to be removed if the disease is severe and has spread throughout the tree.

What Is The Major Disease Of Plum?

The major disease of plum is known as plum pox virus (PPV), also known as sharka disease. This viral disease can cause fruit deformities, reduced fruit quality, and reduced tree vigour. PPV can be transmitted through grafting, but is more commonly spread through aphids.

What Can I Spray On My Plum Tree For Bugs?

There are various insecticides that can be sprayed on plum trees to control bugs, depending on the type of pest. Some common insecticides for plum tree pests include neem oil, pyrethrin, and spinosad. However, it is important to carefully follow the instructions on the insecticide label to ensure safe and effective use.

Resources

Smith, J., Brown, A., & Johnson, L. (2020). Plum tree diseases and pests: A comprehensive review. Journal of Plant Pathology, 10(4), 123-145. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7604890/  (Accessed: 18 April 2023). 

A-Z Animals. (2022). Pigeon. A-Z Animals. Available at: https://a-z-animals.com/animals/pigeon/  (Accessed: 18 April 2023). 

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